The present invention relates to illuminated airfield signs of the type used for marking ground traffic routes on runways and taxiways. The invention is more particularly concerned with an improved airport guidance sign having reduced power consumption, greater reliability and more even illumination across its legend panel(s) than the guidance signs of the prior art.
Illuminated guidance signs are commonly used at airports to identify runways and taxiways and provide ground route marking information for air crews. These guidance signs have transparent or translucent legend panels supported in a frame or case, with the case being supported on legs that provide a minimum ground clearance. Airport runway and taxiway guidance signs are an essential element of airport operation and safety, and are essential for managing ground traffic for airplanes and for maintenance personnel. The sign needs to be clearly visible at all hours, both by air crews and by maintenance crews, and non-dimming, so the illumination needs to be even so that the message on the sign can be clearly distinguished in all ambient lighting conditions and at all viewing angles.
The standards for airport guidance signs in the United States are established by the Federal Aviation Administration. The FAA requires a wind load and frangibility test to ensure that the sign will perform its function under severe wind conditions, but can break off under conditions of extreme force, for example if an aircraft rolls into or over the guidance sign. A frangible connector employed in the mounts for the guidance signs to provide a safe failure mode for the signs so that the danger to the aircraft is minimized. The FAA also requires that the guidance sign meets specifications for photometry, and power source specifications when drawing power from connections to the airfield circuit, i.e., runway and taxiway power.
In double-width, multiple-width, or larger guidance signs, and in those that have curved legend panels, the internal support structure can block the light from the guidance sign lamps, and can create undesirable shadows and bright spots in the legend panels, and this can affect their readability adversely. There have been some attempts to remedy this unevenness of lighting by including additional reflective structure within the frame of the guidance sign. One such attempt is discussed in Hansler et al. U.S. Pat. No. 6,946,975. In the approach that is discussed in that reference, there is a multiple-element light source, with the lamps producing downwardly directed beams. There are prism refractors disposed at the base of the sign, with V-shaped grooves, which are intended to diffuse the incident light so that it is more or less even when it reaches the guidance sign legend panels. While this rather complex design does improve the evenness of lighting somewhat, it does not provide even lighting across the entire panel. Moreover, the power consumption is of that design is rather high.